Secondary data users need three types of knowledge to analyze secondary data: knowledge about data, background knowledge necessary to understand and interpret data, and data analysis skills. Part of knowledge about data is provided by the documentation of data. Background knowledge and data analysis skills are internalized as users' absorptive capacity. When documentation and their absorptive capacity are inadequate, users need to seek outside information to use secondary data. In this paper, causes of inadequate documentation were analyzed, why and how secondary users seek outside information were reported. Then based on the findings, implications about how to facilitate secondary data use were discussed.